USSA-5 Build with Review

Jump to Latest
#881
#883
potstip said:
Bescause i want to use LT3045 / LT 3094 couple to get very clean power source. And 15v output is the limit of regulator.


I asked here below if possible to get 24v from dual output configration

LT3045/LT3094 Positive and negative 24v output - Q&A - Power By Linear - EngineerZone
Click to expand...

The PSU designs readily available on this forum are very quiet and will deliver the current necessary for a power amp design.

I would use the LT3045 for a preamp or dac.

Don't reinvent the wheel.

Cheers,

Greg
 
#885
potstip,

As ggetzoff has correctly mentioned in his post earlier, there are other excellent low noise solutions that will be more appropriate for voltage and load requirements of the USSA 5 power amplifier. My suggestion also would be to look those up.
 
#886
fab said:
Hi nikosokey
I had written a long response but waited too long and it expired so I lost everything😡

. With 1.25A bias current at about +/-24vdc you get in theory 25Wrms class A in 8 ohms and half of that power in class A in 4 ohms. But you get more power in class AB because of your 4 ohms (50Wrms) provided that your psu is capable of delivering it, thus maybe more 40wrms.
With 93db and 4 ohms I would use the same psu parts rating as indicated in the manual but you can reduce psu voltage and increase bias current accordingly to get same heatsink power dissipation. This way you get less max power in class AB (which you probably do not need) but more power in class A.🙂
Having said that the power in class A is more than indicated in reality because of the square law effect of the output mosfet which is increased because of the very low degeneration.

For example with +/- 20 vdc and 1.5A bias you get same heatsink dissipation as with +/-24vdc and 1.25A bias. This gives 18wrms in class A (theory) but probably 25Wrms class A because of previous explanation.

Fab
Click to expand...
Many thanks Fab for explanation...
So the voltage of main trafo supply remain the same 2x18VAC/300VA= about 2x24VDC only we raise the bias at 1.5A and the voltage output going down to 2X18VDC OR we choose smaller voltage of the trafo ?
 

Attachments

  • IMGP0046.jpg
    IMGP0046.jpg
    982.2 KB · Views: 427
  • IMGP0047.jpg
    IMGP0047.jpg
    891.4 KB · Views: 415
  • IMGP0050.jpg
    IMGP0050.jpg
    987.7 KB · Views: 422
#887
Hi nikosokey
Lower transfo voltage such as 15vac or 16vac would give about +/-20vdc or so depending on loading regulation (200-300VA).
However, have in mind that lot of peoples have 4 ohms speakers and still use the +/-24vdc at 1.25A bias and it is just fine since most of the time you listen to less than about 12 or 15 wrms so always in class A. At the same time you get more power in class AB when occasionally needed. This is push pull and not single ended so no real concern here 🙂

Fab
 
#889
Potstip,

You are going to need to do a quad of them. The data sheet states a max input of 22v. You are going to need a least a quad of them to safely deliver that much current. At 500mA. that is MAX current.

However, you will not have proper current delivery with this setup. Just as Fab said, it's not an appropriate part for a power amp nor is it's noise level necessary.

Build the amp with a conventional CRC regulated linear design and enjoy the amp.

The LT3045 would be good for AVCC dac power; anything things that really need to be low noise.

Cheers,

Greg
 
#891
Hi Fab,

May i know what is the max safe rail supply voltage for the USSA5 (mosfet) version?

As i currently encounter unavailability of the 22vac transformer in asia, shipping from USA costs me twice as much as the actual price of the Trans.

So i may use 24vac toroidal instead, but it will produce much higher rail voltages for the USSA5.

Thanks
 
#892
meanie said:
Hi Fab,

May i know what is the max safe rail supply voltage for the USSA5 (mosfet) version?

As i currently encounter unavailability of the 22vac transformer in asia, shipping from USA costs me twice as much as the actual price of the Trans.

So i may use 24vac toroidal instead, but it will produce much higher rail voltages for the USSA5.

Thanks
Click to expand...

You will be fine at your final rail voltage with 24v trafo. Both the input and OPS FETS will be good.
 
#893
Hi meanie
Since you already have an USSA5 do you mean you want to try out the USSA 5.1?
Aside the max specified voltage for parts, attention needs to be done for reasonable power dissipation since this is class A with constant high current. For the same heatsink size to preserve same temperature you would need to reduce output bias accordingly with higher psu voltage. However, doing so will reduce the open loop gain then the damping factor...

As for the driver it is meant to have at least more than 22ma to enter the more optimized operation of the transistor. I would not decrease driver current. However temperature tracking is adjusted for <= +/-28vdc psu. You may need to change a resistor value for optimization....

It would not be exactly the same amp thus will sound different...but how much ....🙄

Fab
 
#895
Ah ok I understand.😛
you will lose some volts for each rail with SLB then. 🙂
Can you check to drop the voltage under 30vdc either by pot adjustment and/or increase R in the CRC? This way you could keep more the original characteristics...
Other option is to keep your actual transfo and live with a little less overall power and even increase class A power with more bias...😉

Fab
 
#897
Well this is a bummer 🙁
In the process of matching Q1,2,3,4 transistors, I found the Mouser bag labeled with BC550CBU is really filled with AD592ANZ temperature sensors 😡
I could use the BC546B/BC556B I have, but the highest hFE is in the 350’s.
Is that acceptable?
 
You must log in or register to reply here.
Top Bottom